Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: G5RV and MFJ 949e Problems  (Read 588 times)
KA5REJ
Member

Posts: 10




Ignore
« on: November 21, 2003, 03:10:18 PM »

I have a G5RV up 35ft. in an inverted vee at a 75 degree angle. The RG213 coax is connected to an MFJ 494e tuner. The ladder line is at a 75 degree angle with the ground. I can only get the SWR down to 2.5 to 1 on 20 meters, but all other frequencies are too far off to transmit. Help?
73s
KA5REJ
ka5rej@comcast.net
Logged
K4AHA
Member

Posts: 1




Ignore
« Reply #1 on: November 21, 2003, 03:26:55 PM »

I had a simular problem.
I improved my ground and the problem went away.
Logged
WB2WIK
Member

Posts: 20635




Ignore
« Reply #2 on: November 21, 2003, 03:34:20 PM »

You've done a few things that will hurt performance of the G5RV, but this shouldn't be disastrous:

35' is a bit too low for a G5RV inverted vee.  In fact, I don't see how it's possible for the included angle between the legs to be 75 degrees as you say, since each leg is 51' long and if installed as an inverted vee with a 75 degree included angle, the ends would be literally on the ground.  That won't work.

You'll have to either install the center higher, or open up the included angle between legs to something broader than 90 degrees, in order for the antenna to function.

Not at all surprised it doesn't load up if installed as you say, since the "ends" of this antenna need to each be several feet above the ground, and insulated with ropes, in order to keep the earth (ground) from closely coupling to these points and end-loading the antenna a great deal.  Such an installation would normally change the resonant frequency of the antenna from 14 MHz (where it's normally a 3/2-wavelength doublet, and a pretty good match) to something well below 14 MHz.

The ladder line should exactly bisect the angle between the legs if at all possible, otherwise the antenna will couple to its feedline.

WB2WIK/6
Logged
K5ENA
Member

Posts: 82




Ignore
« Reply #3 on: November 21, 2003, 03:35:57 PM »

You might try changing you tuner inductor setting to one letter up.  In other words, if your setting is at "I", change the inductor setting to "H".  This could be applicable to the other bands also.  I have had a G5RV at 40 FT for 3 years and found that to be the case with my MFJ 949E when I had it.
Good luck.
73, John, K5ENA
Logged
K5ENA
Member

Posts: 82




Ignore
« Reply #4 on: November 21, 2003, 03:40:09 PM »

I agree with Steve.  The angle of the inverted vee should not be less than 90 degress.  Mine is probably about 100 or 110 degrees.
73, John, K5ENA
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #5 on: November 21, 2003, 09:30:12 PM »

Well, the 75 degrees seems to be throwing everyone for a loop. As is the 2:1 SWR on 20, since that can be interpreted as the best match you can get through your tuner.

However, I suspect you mean the wires are about 15 degrees below horizontal; and you get something close to 2:1 indicated SWR with the tuner straight through. And I have two suggestions for you.

The first is to go to www.radioworks.com and read what someone who makes one of the better versions says about the G5RV.

The second is to add a few feet to your coax. The G5RV has a very high inherent standing wave ratio on all bands except 20 Meters and uses a specified length of coax as a matching transformer. Therefore the feedline length is VERY critical if you are to achieve a low SWR on the other bands.

73  Pete Allen  AC5E
Logged
W8JI
Member

Posts: 9296


WWW

Ignore
« Reply #6 on: November 22, 2003, 10:04:30 AM »

Your antenna should match fine **with** the tuner on nearly all bands, IF the tuner is working correctly and you are following the instructions in the tuner. That assumes all the connections are good in your system.

The angle of the legs has some effect, but won't suddely stop things from working. It and the height will mostly affect how the antenna "gets out", unless you really fold the antenna all back on itself.

Stretched out, a G5RV has lowest SWR on the low end of 80 (where it is about 2 or 3 to 1), just above 40 meters (less than 2:1 but above the band), and on 20. So they work pretty well on those bands.

With the tuner you should be able to make it load up on all other bands, but the efficiency will not be very good on some bands. It will be OK on 80,40, and 20.

I'd suggest you re-read the tuner manual, and double check the connections. As a test if you can't hear signals with good strength, even without the tuner in line, something is wrong.

Even folded into a somewhat tight apex angle, the tuner should be able to handle that antenna...of course you could have run into a problem with MFJ's legendary quality control, and the tuner might not be working....hi hi.

73 Tom
Logged
KC7YRN
Member

Posts: 161




Ignore
« Reply #7 on: November 23, 2003, 05:13:48 AM »

Doesn't "legendary" mean partly history and partly myth?

:-),

Fred
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!